The invention relates to a method for producing a steel product which has a high yield strength. The product according to the invention can, in particular, be a steel sheet or a steel strip.
A light steel used for producing body components and for low temperature use is known from DE 197 27 759 C2. In addition to Fe it contains 10% to 30% Mn, 1% to 8% Al and 1 to 6% Si, the total of the Al and Si contents not exceeding 12%. In this known steel carbon is at best contained in the impurities range.
In the light constructional steel known from DE 199 00 199 A1, on the other hand, carbon is provided as an optional alloy element. The known light steel comprises >7% to 27% Mn, >1% to 10% Al, >0.7% to 4% Si, <0.5% C, <10% Cr, <10% Ni and <0.3% Cu. N, V, Nb, Ti and P may also be contained in the steel, wherein the total of these elements must not exceed 2%.
Steels of the above-described type have TWIP properties (“TWIP”=“Twinning Induced Plasticity”). This property means that they exhibit high ductility while at the same time having good rigidity and a low weight. Accordingly, an extremely good product can be ascertained from tensile strength and elongation for TWIP light constructional steels. In steel sheets produced from known TWIP light constructional steels the minimum yield strength is conventionally in the range of 260 to 330 MPa.
Even higher yield strengths while simultaneously retaining good ductility can, for example, be achieved with TRIP steels (“TRIP”=“Transformation Induced Plasticity”) or in steels in which mixed TWIP and TRIP properties exist. However, all variations of known sheets produced from light constructional steels of this type have specific disadvantageous properties when they have yield strengths of more than 330 MPa. Thus, for example, scatterings of the brittle-ductile transition temperature, temperature-dependent properties or an anisotropic deformation behaviour can occur.